This invention relates to a disc playback device for playing back discs such, for example, as Compact Discs and, more particularly, to a disc playback device capable of continuously playing back a plurality of discs set on a rotary table in the device. Particularly, the invention contemplates to provide a disc playback device of this type in which one can draw out a tray carrying the rotary table and replace discs on the rotary table during playing back of a disc.
Known in the art are disc playback devices according to which a rotary table is provided on a tray and a plurality of discs ar set at a time on the rotary table so as to play back these discs continuously one after another. FIG. 2 shows one of such known disc playback devices. In this playback device, a tray 12 is displaced relative to a main body 10 of the playback device in the directions of arrows Ato be received in or taken out of the main body 10. On the tray 12 is mounted a rotary table 14 which is rotatable in the directions of arrows B. A plurality of disc holding sections 18 are formed about a center of rotation 16. An opening 24 for inserting a turntable and a reproducing head therethrough is formed in each disc holding section 18. A clamper 20 is mounted on the rear end portion of the tray 12. On a chassis 22 in the main body 10 of the playback device are provided elements including the turntable and reproducing head (not shown).
After the tray 12 with the rotary table 14 on which discs are set has been received in the main body 10, the rotary table 14 is rotated to position one of the disc holding sections 18 above the turntable. Then, the turn table and the reproducing head are elevated and inserted into the opening 24. This cause the disc to be lifted by the turntable off the disc holding section 18 and to be clamped by the clamper 20. In this state, the disc can be rotated and played back by the reproducing head. In case discs are continuously played back, the turntable is lowered upon finishing of playback of one disc to restore the disc to the disc holding section 18 and then the rotary table 14 is rotated to position a next disc holding section 18 above the turntable for next playback.
According to the prior art disc playback device, playback of a disc must be stopped if disc set on the rotary table are to be replaced by other discs and it is not possible to draw the tray out of the main body of the device for replacing of disc while continuing playback of a disc.
It is the first object of the invention to provide a disc playback device enabling drawing of a tray out of a main body of the device for replacing of discs while performing playback of a disc.
In this type of disc playback device, it is necessary to detect presence or absence of a disc in each disc holding section of the tray after the tray has been received in the main body and before the discs are played back.
For detecting presence or absence of a disc in each disc holding section, there has been a prior art device in which light-emitting elements and light-receiving elements are provided on the tray in such a manner, that these elements face disc holding sections and a rotary table is rotated by 360 degrees so that presence or absence of a disc in each disc holding section is detected by detecting whether or not light emitted by the light-emitting element and reflected by the disc is received by the light-receiving element.
There is another device is which a rotary table is rotated by 360 degrees in a state in which laser beam is irradiated from a reproducing head (optical pick-up) so that presence or absence of a disc in each disc holding section is detected by detecting whether or not reflected laser beam is received by a light-receiving element in a reproducing head.
The prior art device having the light-emitting and light-receiving elements on the tray for detecting presence of absence of a disc requires the light-emitting elements, light-receiving elements, a drive circuit for driving these elements and a detection circuit respectively provided exclusively for this purpose with a result that the structure of the device becomes complex and the manufacturing cost becomes high.
The prior art device for detecting presence or absence of a disc by utilizing the reproducing head is simiplied in its circuit design. In this device, however, rotation of the rotary table is stopped at each disc holding section and an objective lens of the reproducing head is moved vertically to form a focus on the disc and detect its reflected beam for detecting presence or absence of a disc. The device therefore requires a considerable extra time for stopping rotation of the rotary table and vertically moving the objective lens.
It is, therefore, the second object of the invention to provide a disc playback device capable of detecting presence or absence of a disc in each disc holding section with a simple construction and in a short time.
Further, in this type of disc playback device in which discs on the tray can be replaced by other discs during playback of a disc, there is likelihood that a track jump occurs on a disc which being played back due to a shock caused by moving of the tray out of and into the main body of the device.
It is, therefore, the third object of the invention to provide a disc playback device capable of preventing occurrence of a track jump during playback of a disc due to a shock caused by moving of the tray.